Method for controlling an automated clutch

ABSTRACT

An automated clutch of a motor vehicle is controlled according to a method with the steps:  
     a) determining a first engine rpm-gradient signal (dn m (M)/dt) based on an engine torque signal (M e ) and a target value (M k ) of the clutch torque;  
     b) determining an engine rpm-rate signal (n m (R)) based on the engine rpm-gradient signal from step a);  
     c) comparing an actual engine rpm-rate (n m ) to the engine rpm-rate signal (n m (R)) from step b) and determining a correction quantity K based on the comparison; and  
     d) correcting the first engine rpm-gradient signal (dn m (M)/dt). with the correction quantity K.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of International PatentApplication Serial No. PCT/DE02/01149, filed Mar. 28, 2002, published inGerman, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] The invention relates to a method and apparatus for operating amotor vehicle. The invention further relates to a means for carrying outthe method, and to the use of the method and apparatus in a motorvehicle.

[0003] In particular, the invention relates to devices and methods aswell as the utilization of said devices and methods for the automatedactuation of a unit that forms part of the power train of a motorvehicle, in particular a clutch, a transmission, and/or an engine.

[0004] The state of the art offers opportunities for improvement of theaforementioned devices in particular with regard to their durability,wear resistance, functionality, layout, number of parts, userconvenience, ease of assembly, cost and safety.

OBJECTS OF THE INVENTION

[0005] As a general objective, the invention aims to improve astate-of-the-art device with regard to one or more of the aforementionedcharacteristics, i.e., durability, wear resistance, functionality,layout, number of parts, user convenience, ease of assembly, cost andsafety.

[0006] A specific objective of the invention is to develop a start-upfunction to be used by a control unit for the actuation of the vehicleclutch, so that the start-up, i.e., the transition from a stationary toa moving state of the vehicle, is controlled by engaging the clutch inaccordance with a control target. In this start-up process, a clutchthat is actuated automatically by an actuator unit is controlled throughcontrol command signals in such a manner that the vehicle is set inmotion as the clutch is engaged in accordance with a target function.

[0007] A further objective of the invention is to propose a way ofdetermining and using characteristic quantities such as a friction valuein the control of an automated clutch to achieve an engagement and/ordisengagement of the clutch without unnecessarily long slippage phases.In vehicles with an automated clutch, the value that quantifies theclutch friction (also referred to as friction value) used in the controlprocess can be stored at the times when the control device of theautomated clutch is being shut down, i.e., when turning off the ignitionkey of the vehicle. At a subsequent start-up of the control device, thestored friction value is used in the initialization of the frictionvalue adaptation.

[0008] The invention further has the objective of proposing a way ofcontrolling a clutch so that deviations caused by temperature changeswill not cause the clutch to behave in an uncomfortable or unsafemanner.

SUMMARY OF THE INVENTION

[0009] The invention provides a solution for at least one of theforegoing objectives in a vehicle of the kind described above by makinguse of an observer system or an observer strategy for determining thetime derivative of the engine rpm-rate and for determining the frictionvalue of the clutch.

[0010] The term “observer” in the sense of a technical system is knownin the field of control theory. It means an instrument by which processsignals not captured through measurements can be reconstructed fromobservations of a few of the system's outputs. The best-known embodimentof an observer is the Luenberger observer, a linear model that parallelsthe actual system and is suitable for estimating internal variables of aprocess. As an example, the invention proposes the concept ofdetermining a velocity in a process or system where only the associatedtravel position signal is measured by a sensor.

[0011] For example, state-of-the-art engine control systems of motorvehicles deliver information about the engine rpm-rate by way of acentral area network (CAN) but fail to include the time derivative ofthe engine rpm-rate (also referred to herein as engine rpm-gradient),although the latter is useful or necessary for a diversity of control-and regulating functions in the power train.

[0012] As an approximation of the engine rpm-gradient, one can use thedifference quotient${\frac{n_{m}}{t} \approx \frac{{n_{m}\left( t_{k} \right)} - {n_{m}\left( t_{k - 1} \right)}}{T_{A}}},{wherein}$

[0013] dn_(m)/dt represents the time derivative of the engine rpm-raten_(m)

[0014] n_(m)(t_(k)) represents the engine rpm-rate at a measuring pointk

[0015] n_(m)(t_(k-1)) represents the engine rpm-rate at a measuringpoint k-1

[0016] T_(A)=t_(k)−t_(k-1) represents the time interval from point k-1to point k.

[0017] However, the foregoing solution has the disadvantages of signalnoise and a possible loss of phase information. If a filter is used forsmoothing the signal, this can also lead to a loss of phase information.

[0018] The use of an observer as defined above proves especiallyadvantageous in systems with an automated clutch and/or an automatedtransmission, as it provides a means of also including the currently setclutch torque (besides the engine rpm-rate and the engine torque) in thecalculation of the engine rpm-gradient.

[0019] The principal structure of the observer is illustrated in FIG.3a. The advantage of using an observer according to the illustratedstructure is due to the fact that the determination of the rpm-gradientis not based on the rpm-rate alone, but also includes the torque valueswhich are the cause of an rpm-gradient. Block 209, represented withbroken lines in FIG. 3a can be added as a means of accounting for timelags that may occur in the engine control system between the measurementand the signal transmission of the engine rpm-rate. The sensitivity ofthe observer is set by means of an amplification factor {circumflex over(K)}. It is also possible to expand the observer structure in the senseof a model-based system representation as a means of representingcharacteristic quantities such as the friction value of the clutchduring slip phases.

[0020] The physical friction value, and thus also the value used by thecontrol method, is subject to a relatively strong increase associatedwith a heating-up of the clutch. If the vehicle is switched off whilethe clutch is hot and the physical friction value used by the controlmethod is therefore very high, the friction value used by the controlmethod in a subsequent restart of the vehicle with a cold clutch, e.g.,two to three hours later, will have the same elevated value as it hadwhen the vehicle was last switched off. However, because of thecooling-down of the clutch, the physical friction value of the clutchwill have returned to its normal level. Thus, the vehicle starts runningwith an incorrect friction value being used by the control method. As aresult, the gear shifts are performed with too much slip in the clutch,so that the slip phases during engagement and disengagement of theclutch will be too long. This condition continues until an adaptationroutine used in the control method will have correctly updated thefriction value.

[0021] It is advantageous to use a different way of initializing thefriction value that is to be used by the control system at the start ofthe engine. The initialization can be performed in the following ways:

[0022] 1. The friction value to be used by the control system can beinitialized with a fixed preset value (RW-Init).

[0023] 2. The friction value to be used by the control system can beinitialized with a value that depends on how long ago the engine waslast turned off. The friction value that was in effect at the time theengine was turned off converges towards a nominal preset value (RW-Init)to an extent that depends on the elapsed time since the engine wasturned off.

[0024] 3. The friction value to be used by the control system can beinitialized with a value that is a function of the temperature. Based ona temperature model that also allows a clutch temperature to bedetermined, it is possible to determine the temperature decrease thatoccurred between the time the engine was switched off and the time thecontrol system is switched on again. The initializing value for thefriction value could be determined through this temperature model.Analogously, one could use the radiator temperature, the enginetemperature, or a similar characteristic variable that may be availableto the control device.

[0025] 4. The friction value to be used by the control system can beinitialized with a value that is based on a characteristic data array.This array, curve, or curve field can be a function of the time elapsedsince the engine was last turned off, or a function of the temperaturedecrease of the engine or of the clutch.

[0026] 5. The friction value to be used by the control system can beinitialized with a nominal initialization value (RW_Init) which,according to the invention, can be determined in at least one of thefollowing ways:

[0027] a) The initialization value is set as a fixed value, e.g., as asubstitute friction value, or by using a nominal initialization value.

[0028] b) The nominal initialization value can be adapted, e.g., byredetermining the nominal initialization value at set time intervals.

[0029] c) The nominal initialization value can be adapted at certaintemperatures, for example only in the range between 80° C. and 100° C.,so that the friction value matches the situation at the start of theengine.

[0030] d) In addition, if an adaptation of the nominal initializationvalue is made, it can be limited to a small change in order to avoid therisk of erroneously making a big change.

[0031] It can also be advantageous to use combinations of the foregoingconcepts.

[0032] It is advantageous to perform an initialization of the frictionvalue at the time the ignition is switched on, especially in a casewhere it can be expected that the current friction value has changedsubstantially from the friction value that was determined and adapted inthe operating phase that ended when the ignition was last switched off.Thus, it is recommended to perform an initialization of the frictionvalue when certain conditions indicate that the friction value may havechanged. As a means of detecting at least one such condition, thecurrent clutch temperature at the end of an operating phase is stored ina memory such as an EEPROM. When the ignition is subsequently switchedon again, the stored temperature is retrieved from the memory device andcompared to the current clutch temperature. If a large difference isfound between the two temperatures, the friction value should bereinitialized.

[0033] The current clutch temperature can be calculated, e.g., by meansof a temperature model, or it can be measured with a temperature sensor.At least one of the following signals may be used to determine theclutch temperature: transmission temperature, engine temperature,outside temperature, elapsed time since the engine was last turned off,and engine coolant temperature. For cost reasons, it may for example beadvantageous to have no clutch temperature sensor, but to calculate theclutch temperature based on at least one of the existing temperaturesensors of the motor vehicle and using an appropriate temperature model.

[0034] It has been found that the friction value used in the controlprogram for calculating the transmittable torque clutch has an influenceon the clutch temperature and vice versa. If the friction value is notadapted over an extended time interval, there may nevertheless be achange in the clutch temperature. This is possible, e.g., in thefollowing situations:

[0035] if the vehicle engine is turned off;

[0036] in a hybrid-drive vehicle, if the electric motor alone is used asa drive source over an extended time period;

[0037] if gear shifts are performed with the clutch engaged, so thatthere is no opportunity for adaptation during gear shifts, for examplein a hybrid-drive vehicle or in a vehicle with a power-shifttransmission, i.e., a transmission that is capable of transmittingtorque during gear changes.

[0038] If the control program uses an incorrect friction value in thestart-up of the vehicle or in the clutch re-engagement after a gearchange, this may result in oscillations of the power train and in adiminished level of driving comfort.

[0039] It is advantageous to establish a functional dependence betweenthe temperature and the friction value:

Rw=function1(RwTU, TcC),  (1)

[0040] wherein Rw represents the temperature-dependent friction valuethat is used for the control of the clutch in all calculations, forexample to determine values of the clutch torque. RwTU is thetemperature-independent portion of the friction value, and TcCrepresents the current clutch temperature. The inverse of the foregoingfunction, i.e.,

RwTU=function2(Rw, TcC),  (2)

[0041] should also be established, so that the temperature-independentportion of the friction value can be determined from the currentfriction value Rw.

[0042] The functions 1 and 2 may be arithmetically defined orrepresented by value tables. In a practical implementation, thefunctional correlation between Rw and RwTU could be represented througha temperature-dependent correction factor:

Rw=RwTU×F(TcC)  (3),

and

RwTU=Rw/F(TcC)  (4).

[0043] The values Rw and RwTU are stored in memory, e.g., in an EEPROM,at the time of turning off the ignition. The value RwTU depends, e.g.,on the type of friction liner that is used in the clutch, on the stateof wear, and also on the degree of humidity of the friction liner,making it necessary to provide a possibility of also adapting the valueof RwTU. The value of Rw is advantageously adapted during the start-upof the vehicle or during the re-engagement of the clutch after a gearchange.

[0044] As a concept of the invention, it is proposed to initialize thetemperature-dependent friction value Rw after a system start and at eachstart-up of the vehicle as well as prior to re-engaging the clutch, forexample in accordance with equation (1) or equation (3). As this couldresult in an abrupt change of the friction value Rw, which could cause asudden change of the clutch torque, it is practical to perform thisinitialization only in situations where a sudden change of the clutchtorque has no critical consequences. It is therefore preferable toperform the initialization or provisional adaptation of the frictionvalue for example at a time when the clutch is completely engaged, forexample at a system start or with each volume adjustment of a hydrauliccircuit such as a fluid replenishment through a snifting conduit, and/orwhen the clutch is completely out of engagement, and/or when the clutchis transmitting a minimal amount of torque.

[0045] After a complete adaptation, the temperature-independent portionof the friction value can be updated in accordance with equation (2) orequation (4). Preferably, this inverse adaptation of thetemperature-independent value is not performed directly but by way of afilter, in order to avoid strong fluctuations of thetemperature-independent value RwTU. It is further possible to use atwo-stage filter with different time constants. The result of theshort-term filtering operation, RwTU1, would represent short-termchanges of the friction value caused, e.g., by high levels of humidity.The value RwTU1 is in effect only for one trip of the vehicle and isreset to the long-term value at each system start. The long-term valueRwTU2 represents the result of the long-term filtering process andcontains that part of the temperature-independent value which changesonly as a result of aging. An adaptation of the temperature-independentfriction value can be suppressed for example at extremely low orextremely high values of the clutch temperature for which thetemperature dependence of the friction value may not be reliably known.To ensure a correct initialization at the system start, a reliableestimated value for the clutch temperature must be available at thatpoint in time. Vehicles with an automated transmission and/or anautomated clutch employ a so-called friction value adaptation, whereinthe friction value is determined mathematically from operating variablesand continuously adapted in the control program, i.e., updated on thebasis of current data so that it reflects the currently effectivephysical friction value of the clutch. To perform this adaptation, thecurrently transmitted friction torque M(K) can be determined from theengine torque M(M) and the inertial torque M(B) which consists of themultiplication product of the rotary engine acceleration and theeffective mass moment of inertia of the crankshaft and flywheel:

M(K)=M(M)−M(B)

[0046] If the adaptation delivers a friction value that is too low, forexample due to erroneous torque signals or other inaccuracies, thebuild-up of clutch torque after each gear shift will be too strong. As aresult, the clutch will pass through the slipping phase very quickly, sothat the gear shift may in some cases be accompanied by a jolt. In everyslipping phase after a gear shift, the friction value is alwaysre-adapted to the new conditions. If the error or inaccuracy in thetorque signals disappears, the calculated clutch torque will return to abetter agreement with the physical values, and the calculated frictionvalue is brought back into agreement with the physical friction value bymeans of the adaptation procedure. After an error has been introducedinto the adapted friction values, the subsequent adaptation cycles willbe subject to an undesirable hysteresis.

[0047] In order to avoid errors of this kind in the adaptation, theinvention introduces a measure based on the experience that with acorrectly adapted friction value, the duration of the clutch slippage isnearly constant for each engagement process. It is therefore proposed todetect and evaluate the duration of the clutch slippage at theengagement of the clutch. If a deviation of the slippage time intervalfrom a reference value is detected, this serves as an indication oferrors in the torque signals and as a result, the program will change toan emergency adaptation mode for the friction value. The emergencyadaptation can be made with signals other than the erroneous torquesignals. If the friction value is correct, the slippage time intervalafter a gear shift as a function of gas pedal depression will beconstant. Although the slippage time interval depends on additionalfactors such as the grade angle of the road and/or the presence andweight of a trailer, it is possible to eliminate the influence of thesefactors through appropriate adjustments. It is advantageous to determinethe friction value through an emergency adaptation, if the slippage timeduration exceeds a certain time limit that depends on the amount of gaspedal depression. The correlation between slippage time and emergencyadaptation of the friction value can be based on a mathematicalfunction. A linear correlation may be particularly advantageous where alarger friction value is to be determined in case of a longer slippagetime interval. Thus, this kind of adaptation is not based on the enginetorque and the rotary acceleration of the engine, but on the slippagetime duration and on the pedal depression:

[0048] Friction value=f(slippage duration, pedal depression, . . . )

[0049] According to a further concept of the invention, the adaptationof a friction value is determined on the basis of the clutchtemperature. For example, if a clutch is heated up rapidly within ashort time, the friction value of the clutch changes. To provide acompensation for this phenomenon, it is advantageous to perform afriction value adaptation in a software program for the clutch control.To ensure the stability of the adaptation routine in the control programand to limit the influence of transient extremes of the clutchtemperature as measured, e.g., directly by means of a clutch temperaturesensor or determined indirectly from other parameters such as thesignals of other temperature sensors, the transmitted clutch torque, orthe engine torque, it is practical to set a limit for the change of thefriction value, meaning that the friction value can change by no morethan a given amount per unit of time. If the adaptation program routineresults in a larger change, the value delivered by the program islimited to the given maximum.

[0050] However, if the clutch temperature rises very rapidly, theadaptation of the friction value may be too slow. Nevertheless, it isnot recommended to raise the general limit for the rate of change of thefriction value because of the risk that this could make the adaptationprocess unstable.

[0051] If the adaptation of the friction value is too slow, the build-upof clutch torque will not be strong enough after gear shifts or whenstarting up from a stand-still, i.e., the clutch will have too muchslippage.

[0052] According to a concept of the invention, the limit for themaximum rate of change of the friction value is made dependent on theclutch temperature.

[0053] If the clutch temperature rises rapidly, this can be taken intoaccount in the adaptation of the friction value by raising the limit forthe maximum rate of change of the friction value, for example by apredetermined fixed amount. The limit for the maximum rate of change ofthe friction value can also be raised by an amount that depends on themagnitude of the rate of temperature increase. The correlation betweenthe clutch temperature of its rate of increase and the limit for themaximum rate of change of the friction value can be based on amathematical formula. It is particularly practical to use a linearcorrelation, i.e., the higher the clutch temperature the higher thelimit that is set for the maximum rate of change of the friction value.

[0054] According to a further concept of the invention, the adaptationof the friction value at the start-up of the vehicle can be influencedin a positive sense. If the vehicle is switched off at a time when theclutch is hot and the adapted friction value is therefore low, and theignition is turned on again after the clutch has cooled down, thefriction value used in the control program will be in error, i.e., toolow. As a remedy for this, it can be advantageous to not correlate thefriction value directly to the clutch temperature or its rate of change,but to introduce a factor and/or offset quantity into the correlationwhich is varied dependent on the temperature. For example, the factorcan be set to 1 and the offset to 0 when the ignition is switched onagain. In addition to using a factor or additive offset, it is alsopossible to store the information that the clutch was hot when theignition was switched off. In this case, the limit for the maximum rateof change of the friction value can likewise be increased at the timethe ignition is switched on again. This has the result that the frictionvalue which starts out too small is adapted more rapidly to the physicalfriction value.

[0055] According to a further concept of the invention, the excessiveamount of slippage can be eliminated if an integrating component in thecontrol program is activated also in start-up phases.

[0056] To prevent a negative effect on the start-up behavior which canoccur with the last-mentioned concept, it is practical if theintegrating component is activated only when the clutch temperature isabove the given threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In the following, the invention will be described in more detailbased on embodiments illustrated in the drawings, wherein:

[0058]FIG. 1 represents a first example of a vehicle that canincorporate the invention;

[0059]FIG. 2 represents a second example of a vehicle that canincorporate the invention;

[0060]FIGS. 3a and 3 b represent block diagrams of an observer; and

[0061]FIGS. 4a and 4 b represent graphs of functional correlations.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0062]FIG. 1 represents a schematic view of a vehicle 1 with a drivesource 2 such as a motor or combustion engine. Also shown in the powertrain of the vehicle is a torque-transmitting system 3 and atransmission 4. The torque-transmitting system 3 in this example isarranged at a place in the torque-flow path between the engine and thetransmission. The drive torque generated by the engine is transmitted byway of the torque-transmitting system to the transmission and from thetransmission 4 downstream through a drive shaft 5 and a driving axle 6to the wheels 6 a.

[0063] The torque-transmitting system 3 is configured as a clutch, suchas a friction clutch, a laminar disc clutch, magnet-powder clutch orconverter-bypass clutch. The clutch can be self-adjusting as well aswear-compensating. The arrangement 4 with the transmission includes forexample a manual shift transmission that can be shifted betweendifferent gear stages. However, in keeping with the general concept ofthe invention, the transmission can also be an automated shifttransmission in which the shifting is performed by means of at least oneactuator. The term “automated shift transmission” further encompasses anautomated transmission that is shifted with an interruption in thetractive force and in which the shifting process is performed by meansof at least one actuator.

[0064] Furthermore, an automatic transmission may also be used, wherethe term “automatic transmission” means a transmission that shiftssubstantially without an interruption in the tractive force and which,as a rule, is based on planetary gear stages.

[0065] As a further possibility, a continuously variable transmission,such as a cone-pulley transmission, may be used. The automatictransmission could also be equipped with a torque-transmitting system 3,such as a clutch or a friction clutch, arranged on the downstream sideof the power train. The torque-transmitting system can further beconfigured as a start-up clutch and/or reverse drive clutch and/orsafety clutch in which the amount of torque transmitted can becontrolled to meet a targeted value. The torque-transmitting device canbe a dry friction clutch, or a wet friction clutch operating, e.g., in afluid, or it can also be a torque converter.

[0066] The torque-transmitting system 3 has an upstream side 7 and adownstream side 8 in relation to the flow of torque in the power train.Torque is transmitted from the upstream side 7 to the downstream side 8when a compressive contact force is applied to the clutch disc 3 a bymeans of the pressure plate 3 b, the diaphragm spring 3 c, the releasebearing 3 e as well as the flywheel 3 d. The compressive force isapplied and removed through the release lever 20 by means of an actuatordevice.

[0067] The torque-transmitting system 3 is controlled by means of acontrol system or controller device 13 which may include the electroniccontrol module 13 a and the actuator 13 b. In another advantageousdesign, the actuator and the electronic control module may beaccommodated in two different assembly units or housings.

[0068] The controller device 13 can include the control and powerelectronics for the electric motor 12 of the actuator 13 b. Thisconfiguration allows an advantageous spatial arrangement where space isneeded only for the actuator and associated electronics. The actuatorhas a drive motor 12 such as an electric motor which acts on amaster-cylinder 11 through a gear mechanism, e.g., a worm gear, spurgear, crank mechanism or a screw spindle drive. The motor can interactwith the master cylinder either directly or through connecting rods.

[0069] The movement of the output element of the actuator, such as themaster cylinder piston 11 a, is detected by a clutch displacement sensor14 which registers the position, speed, or acceleration of a quantitythat is in a proportional relationship to the position or degree ofengagement, or the speed or acceleration of the clutch. The mastercylinder 11 is connected to the slave cylinder 10 by way of a pressuremedium conduit 9 such as a hydraulic line. The output element 10 a ofthe slave cylinder is operatively connected with the release lever orreleasing means 20, so that a movement of the output element 10 a of theslave cylinder will, in turn, cause the releasing means 20 to move ortilt in order to control the amount of torque that is transmittedthrough the clutch 3.

[0070] The actuator 13 b for controlling the amount of torquetransmitted through the torque-transmitting system 3 can be designed towork through the action of a pressure medium, i.e., it can be equippedwith master and slave cylinders for the pressure medium. The choice ofpressure media includes, e.g., hydraulic and pneumatic media. The mastercylinder may be actuated by means of an electric motor 12, e.g., underelectronic control. The actuator 13 b may also be driven by a powersource other than an electric motor, e.g., by a hydraulic drive source.It is further conceivable to use magnetic actuators to control aposition of an element.

[0071] In a friction clutch, the control of the amount of torque thatcan be transmitted is performed by applying a controlled amount ofpressure on the friction linings of the clutch disc between the flywheel3 d and the pressure plate 3 b. The amount of force on the pressureplate, and thus the pressure on the friction linings, is controlledthrough the position of the releasing means 20, e.g., a release fork ora concentric slave cylinder, whereby the pressure plate can be moved toand maintained at any position between two end positions. One endposition corresponds to a completely engaged clutch position, while theother end position corresponds to a completely disengaged clutchposition. To set the clutch so that it will transmit a torque of, e.g.,lesser magnitude than a currently delivered engine torque, the pressureplate 3 b can for example be set to a position corresponding to anintermediate range between the two end positions. With the controlledactuation of the releasing means 20, the clutch can be fixed at thisposition. However, the clutch can also be enabled to transmit amounts oftorque exceeding the actually delivered engine torque by a definedmargin. This allows the currently available amounts of engine torque tobe transmitted, while torque fluctuations in the power train, e.g., inthe form of transient peak amounts of torque, are damped and/orisolated.

[0072] To run the torque-transmitting system, in the sense ofcontrolling or regulating the amount of torque, the relevant operatingquantities of the entire system are at least during part of the timemonitored by sensors that deliver the current status data, signals andmeasurement values required for the control. This information isprocessed by the control unit, and there can also be a signal connectionto other electronic units, e.g., electronic modules associated with theengine or an anti-lock braking system (ABS) or an anti-slip regulationsystem (ASR). The sensors perform the functions of, e.g., detectingrpm-rates such as wheel rpm-rates and engine rpm-rates, the position ofthe gas pedal, the throttle valve position, the gear position of thetransmission, an intent of the driver to shift gears, and othervehicle-specific characteristic quantities.

[0073]FIG. 1 illustrates a vehicle in which a throttle-valve sensor 15,an engine-rpm sensor 16 as well as a speed sensor 17 are used and aretransmitting measurement values and other information to the controlunit. The electronic module, e.g., a computer module, of the controlunit 13 a serves to process the system input quantities and to transmitcontrol signals to the actuator 13 b.

[0074] The transmission is configured, e.g., as a gear-shiftingtransmission in which the ratio levels are changed by means of a shiftlever, or the transmission is actuated or operated by means of the shiftlever. Furthermore, a sensor 19 b is arranged at the operating lever orshift lever 18 of the manually shiftable transmission. The sensor 19 bserves to detect an intent of the driver to shift gears and/or to detectthe current gear position and to transmit this information to thecontrol unit. The sensor 19 a is connected to the transmission andlikewise performs the functions of detecting a current gear positionand/or an intent of the driver to shift gears. The detection of anintent to shift gears by means of at least one of the sensors 19 a, 19 bcan be achieved by designing the sensor as a force sensor to detect whena force is applied to the shift lever. The sensor could also beconfigured as a displacement sensor or position sensor, where thecontrol unit would be programmed to determine the presence of an intentto shift if a change has been found in the position signal.

[0075] The control unit is in signal communication with all of thesensors at least at certain times and evaluates the sensor signals andsystem input quantities in such a manner that the control unit sendscontrol or regulation commands to the at least one actuator dependent onthe current operating point of the system. The drive source 12 of theactuator, such as an electric motor, receives from the clutch-actuatorcontrol unit a control target signal that depends on measurement valuesand/or system input quantities and/or signals of the associated sensors.The control unit contains a control program implemented in hardware orsoftware to evaluate the incoming signals and to calculate or determinethe output quantities based on comparisons and/or functions and/orfields of characteristic curves.

[0076] It is advantageous if modules are implemented in the control unit13 to acquire data on torque, gear position, slippage and or operationalstatus, respectively, or if the control unit 13 is in signalcommunication with at least one of the aforementioned modules. Themodules can be implemented as control programs in hardware and/orsoftware to determine on the basis of the incoming sensor signals howmuch torque is produced by the drive source 2 of the vehicle 1, whatgear position the transmission is in, how much slippage is occurring inthe torque-transmitting system, and what is the current operating stateof the vehicle. From the signals of sensors 19 a and 19 b, thegear-position detector unit determines which gear is currently active inthe transmission. The sensors 19 a and 19 b are operatively connected tothe shift lever and/or the internal gear-shifting means inside thetransmission, such as for example a central shifting shaft or shiftingrod, where the sensors serve to detect for example the position and/ormovement of these transmission elements. Further, a load-lever sensor 31such as a gas pedal position sensor can be attached to the load lever 30(such as a gas pedal) to detect the load-lever position. A furthersensor 32 can function as an on/off switch that is on or off dependingon whether the gas pedal is active or inactive, so that the binaryon/off signal indicates whether the engine-load control lever, such as agas pedal or accelerator pedal, is currently being actuated. Theload-lever sensor 31, on the other hand, provides a quantitativedetermination of the degree of load-lever actuation or gas pedalactuation.

[0077] In addition to the accelerator or gas pedal 30 (or engine-loadcontrol lever) with the associated sensors, FIG. 1 shows abrake-actuating element 40 for the main brake or the parking brake, suchas a brake pedal, hand-brake lever, or a hand- or foot-operated parkingbrake actuator. At least one sensor 41 is arranged at the actuatorelement 40 to monitor its operating state. The sensor 41 may for examplebe a binary detector such as a switch that indicates whether or not theactuator element is on or off. A signal device such as a brake light canbe connected to the sensor to provide an indication that the brake isbeing applied. This arrangement could be used for the main brake as wellas for the parking brake. However, the sensor can also be configured asan analog sensor such as a potentiometer, to indicate the degree ofapplication of the actuator element. The analog sensor, likewise, can beconnected to a signal device.

[0078]FIG. 2 gives a schematic illustration of a power train of avehicle with a drive source 100, a torque-transmitting system 102, atransmission 103, a differential 104 as well as drive axles 109 andwheels 106. The torque-transmitting system 102 is arranged on orattached to a flywheel 102 a which, as a rule, is equipped with astarter gear rim 102 b. The torque-transmitting system has a pressureplate 102 d, a clutch cover 102 e, a diaphragm spring 102 f, and aclutch disc 102 c with friction linings. A clutch disc 102 c, in somecases with a damper device, is interposed between the pressure plate 102d and the flywheel 102 a. An energy-storing device such as a diaphragmspring 102 f pushes the pressure plate axially against the clutch disc.A clutch actuator element 109 such as, e.g., a pressure-medium operatedconcentric release device, serves to actuate the torque-transmittingsystem. A release bearing 110 is arranged between the concentric releasedevice and the tongues of the diaphragm spring 102 f. When the releasebearing moves in the axial direction, is pushes against the diaphragmspring and thereby disengages the clutch. The clutch can be configuredeither as a push-actuated or pull-actuated clutch.

[0079] The actuator 108 is an actuator of an automated gear-shiftingtransmission and also contains an actuator unit for thetorque-transmitting system. The actuator 108 serves to actuate shifterelements internal to the transmission such as, e.g., a shifter cylinderor shifter rods or a central shifter shaft of the transmission. Theactuator may allow the gears to be engaged and disengaged in sequentialorder of gear ratio, or also in an arbitrary order. The clutch actuatorelement 109 is actuated by way of the connection 111. The control unit107 is connected to the actuator by way of the signal connection 112.The signal connections 113 to 115 summarily represent connectionsleading to the control unit 107, where the line 114 conducts incomingsignals, the line 113 conducts outgoing control signals, and the line115 represents, e.g., a data bus connection to other electronic units.

[0080] To set the vehicle in motion from a stand-still condition or aslow rolling condition or crawl state, i.e., to initiate an accelerationof the vehicle under the control of the driver, the latter in essenceonly depresses the gas pedal, such as the load control lever 30, as theautomated clutch control or regulation takes charge over setting theamount of torque that is transmitted through the torque-transmittingsystem in a start-up phase. The desires of the driver for more or lessacceleration are detected by the engine-load lever sensor 31 based onthe position of the accelerator pedal and are subsequently put intoeffect by the control unit. The gas pedal position and the sensorsignals are used as input quantities for controlling the start-upprocess of the vehicle.

[0081] During a start-up phase, the amount of torque to be transmitted,i.e., the target amount for the clutch torque M_(Ctarget), isessentially determined by means of a predetermined function or fromcharacteristic curves or curve fields which are, for example, dependenton the engine rpm-rate.

[0082] In a start-up phase, substantially from stand-still or from acrawl state, if the load lever or gas pedal is depressed by a certainamount a while the vehicle is moving at a slow speed, the motor controlunit 40 will direct the engine to produce a certain amount of torque.The control unit of the automated clutch actuator 13 in a correspondingmanner controls the amount of torque to be transmitted by the clutch inaccordance with preset functions or data arrays, so that a stationarystate of equilibrium sets in between the engine torque and the clutchtorque. The state of equilibrium is characterized dependent on the loadlever position a by a defined start-up rpm-rate, a start-up enginetorque as well as a defined amount of transmittable torque of thetorque-transmitting system and a defined amount of torque transmitted tothe driving wheels. The representation of the start-up torque as afunction of the start-up rpm-rate will be referred to as start-upcharacteristic in the following discussion. The load lever displacementa is of a proportionate amount as the displacement of the throttle valveof the engine.

[0083] In addition to the gas pedal 122 or other engine load controllinglever with an associated sensor 123, FIG. 2 shows a brake-actuatingelement 120 for actuating the main brake or the parking brake, such as abrake pedal, a hand-brake lever or a hand- or foot-actuated operatorelement of the parking brake. At least one sensor 121 is arranged at theactuator element 120 to monitor the degree of actuation of the latter.The sensor 121 is configured, e.g., as a binary sensor such as a switch,detecting whether the actuator element is on or off. This sensor can bein signal communication with an indicator device such as a brake light,which signals whether or not the brake is being applied. This conceptmay be used for the main brake as well as the parking brake. However,the sensor can also be configured as an analog sensor, e.g., in the formof a potentiometer, to determine the degree of activation of theactuator element. This sensor, too, can be in signal communication withan indicator device.

[0084]FIG. 3a represents a block diagram to illustrate how a timegradient (rate of change) dn_(m)/dt of the engine rpm-rate is determinedby means of an observer 201 on the basis of an engine rpm-rate n_(m) anda torque variable M during a slipping phase of a friction clutch. Thetorque variable M is calculated in a comparator unit 203 as thedifference between a torque signal M_(e) and a torque target M_(k),where M_(e) represents a torque quantity provided by the engine controldevice, for example by way of a CAN bus, which can be determined from acharacteristic data array of the engine and other parameters such as,e.g., the position of the throttle valve. The torque M_(e) representsthe amount of engine torque that is currently being delivered by theengine at the given rpm-rate n_(m). M_(k) represents the targeted amountof torque to be transmitted through the clutch during a slipping phase.The value of M_(k) can be determined in the clutch control device basedon input quantities such as, e.g., the currently engaged gear, thetransmission input rpm-rate, the transmission output rpm-rate, a driverinput indicating an intention to shift gears, and other factors. In asubsequent block 202, the rpm gradient dn_(m)(M)/dt which can beattributed to the torque quantity M is calculated as a quotient of atorque and an effective mass moment of inertia of the engine, using theappropriate conversion factor between an angular acceleration and anrpm-gradient. In the next following step 204, a correction value K isapplied to the result of step 202 to obtain the rpm-gradient dn_(m)/dtas a result. At the branch point 205, the rpm-gradient dn_(m)/dtcontinues along two separate branches, i.e., an output branch 206 and arecursion-loop branch 207, where both branches use the value of therpm-gradient dn_(m)/dt. In the recursion-loop branch 207, therpm-gradient is integrated to obtain a recursive value n_(m)(R) which ina further block 209 can be subjected to a compensation of the time lagthat may exist between the times when the engine rpm-rate n_(m) ismeasured and when the rpm-signal is transmitted, so that a time offsetbetween the engine rpm-rate n_(m) and the recursive value n_(m)(R) canbe prevented or minimized. Analogous to the block 209, it is understoodthat one could also insert a compensating block ahead of the comparatornode 203 to perform an analogous compensation of the torque signal M_(e)that is, either as an alternative or in addition to the compensation inblock 209. In the comparator node 210, the difference between the enginerpm-signal n_(m) and the recursive value n_(m)(R) is determined andtransmitted as an rpm-rate correction n_(m)(K) to block 211, from whicha correction value K is sent to the comparator node 204. At 204, thecorrection value K is added to the rpm-gradient dn_(m)(M)/dt to form therpm-gradient dn_(m)/dt.

[0085] In comparison to the power train observer 201 of FIG. 3a, thepower train observer 301 shown in FIG. 3b has several possible additionsand variations. The signals that are useful or necessary for controllinga power train of a vehicle 1 (see FIG. 1), for example with at least oneautomated clutch and a gear-shifting transmission, can be generated orcorrected under a uniform concept. In the example of the embodiment of apower train observer illustrated in FIG. 3b, the effective engine torqueM_(e), the transmitted clutch torque M_(k), the overall torque M_(F)opposing the movement of the vehicle, the mass moment of inertia J_(M)of the engine, the mass of the vehicle represented as an equivalent massmoment of inertia J_(F), the engine rpm-rate n_(m), the wheel rpm-raten_(F) from which the travel velocity could be calculated, or the travelvelocity of the vehicle as well as the overall ratio i of thetransmission which depends on which gear is engaged.

[0086] Based on a mathematical model for this embodiment, the enginerpm-gradient dn_(m)/dt and the vehicle rpm-gradient dn_(F)/dt (forexample based on the wheel rpm-rate or the rpm-rate of a rotating shaftin the transmission that is correlated to the wheel rpm-rate through aratio factor) conform to the following equations: $\begin{matrix}{\frac{n_{m}}{t} = {{\frac{30}{\Pi} \cdot \frac{1}{J_{M}}}\left( {M_{e} - M_{k}} \right)}} & (1) \\{\frac{n_{F}}{t} = {{\frac{30}{\Pi} \cdot \frac{1}{J_{F}}}\left( {{i\quad ({gear})\quad M_{k}} - M_{F}} \right)}} & (2)\end{matrix}$

[0087] The transmitted clutch torque M_(k) and the movement-resistingtorque M_(F) are essential quantities for the control of automated shifttransmissions as well as automated clutches but are as a rule notmeasurable. These quantities are determined by means of the power trainobserver 301 shown in FIG. 3b.

[0088] The quantities that are supplied as inputs to the observer in theillustrated embodiment are the engine rpm-rate, the wheel rpm-raten_(F), the effective engine torque M_(e) as well as a signal G thatindicates which gear is currently engaged. The power train observer 301is functioning preferably as a PI-observer, i.e., using proportional andintegrating transfer components, in the form of a so-called perturbationobserver. The basic idea behind this approach is to treat thetransmitted clutch torque M_(k) and the movement-opposing torque M_(F)as unknown “perturbations”.

[0089] Based on the engine torque M_(e) that is given as a controltarget and the most recent estimated values for M_(k) and M_(F), theequations (1) and (2) are continuously recalculated in the observer,wherein stored values can be used for the unknown quantities. Severaldifferent initialization measures are proposed to provide plausiblestarting values for the estimated quantities M_(k)(R), M_(F)(R) andn_(m)(R) at the time when the control device is switched on. Inprinciple, the estimates could be initialized with start values of zero,if the relatively long convergence phase until the observer has reacheda sufficient approximation are of no concern. Preferably, the followingvalues can be used for the initialization:

[0090] n_(m)(R)=n_(m) and n_(F)(R)=n_(F)

[0091] The estimate of M_(k)(R) can advantageously be initialized asfollows:

[0092] by using the current engine torque Me as the starting value forM_(k)(R);

[0093] if the clutch is in a slipping condition, by using the currentclutch position as a basis for estimating a starting value for M_(k)(R);

[0094] by using the estimated value for M_(k)(R) that was last stored(e.g., in an EEPROM) in the previous operating phase.

[0095] The estimate of M_(F)(R) can advantageously be initialized:

[0096] by estimating the starting value based on the current wheelrpm-rate;

[0097] by starting with the estimated value for M_(F)(R) that was laststored (e.g., in an EEPROM) in the previous operating phase.

[0098] After the initialization, the program runs in a cycle that can bebased on a given clock frequency. In the node 331, the torque differencethat accelerates the engine is calculated in each cycle from theeffective engine torque M_(e) and the estimated value M_(k)(R). Theresult is passed on to block 302, where an estimate of the enginerpm-gradient dn_(M)(R)/dt is calculated by taking the effective massmoment of inertia of the engine into account. At the node 310, theestimate for the engine rpm-gradient dn_(M)(R)/dt is corrected with acorrection value dn_(M)(R′)/dt. The result from node 310 is integratedin block 308. The result of the integration represents an estimatedengine rpm-rate n_(M)(R), which is compared to the measured enginerpm-rate n_(M) in the program node 304 to determine an error signale_(M).

[0099] In block 322, an estimated value of the wheel rpm-gradientdn_(F)(R)/dt is calculated from the estimated quantities M_(k)(R′) andM_(F) (R), after they have been tied together in the node 333. Theestimated value M_(k)(R′) represents the clutch torque after it has beenconverted in the transmission, i.e., M_(k)(R′) is calculated in block332 based on the estimated clutch torque M_(k)(R) and the parameter Gthat identifies the currently engaged gear. The estimated torque valueM_(F)(R) represents the resistance that opposes the movement of thevehicle. The wheel rpm-gradient dn_(F)(R)/dt is corrected in node 320with the correction quantity K(R) and passed on to the box 328 where thewheel rpm-rate n_(F)(R) is determined as the time integral and passed onto node 324 for comparison with a wheel rpm-rate n_(F) that has beenmeasured or determined by another method. The result of the comparisonis an error signal e_(F).

[0100] The error signals e_(M), e_(F) are used to continuously updateand correct the estimated values of the observer. In the illustratedembodiment of FIG. 3b, this function is performed by four correctorblocks L1, L2, 350, and L3, each of which has an input for e_(M) and aninput for e_(F). Each corrector block amplifies and applies weights tothe error signals in relation to each other. Block L1 combines the errorsignals into a correction value dn_(M)(R′)/dt that is fed back directlyto the node 310, and Block L3 combines the error signals into acorrection value dn_(F)(R′)/dt that is fed back directly to the node320. This serves to stabilize the observer overall, in order to preventoscillations of the control loop. The output quantity from block L2 isintegrated in block 330 to establish an estimate M_(k)(R) of thetransmitted clutch torque. Preferably, the values of the parameters usedin the blocks L1, L2, L3 are selectable based on certain operatingconditions, e.g., the currently engaged gear, the actuation of the gaspedal or brake pedal, the travel speed, and similar factors.

[0101] The corrector block 350 generates an estimated value M_(F)(R) ofthe movement-opposing torque, which is corrected with the error signalse_(M), e_(F). The movement-opposing torque may, e.g., account for airresistance, grade angle of the road, and braking torques.

[0102] In a further preferred embodiment of a power train observeraccording to FIG. 301, the movement-opposing torque M_(F)(R) is split upinto different components:

M _(F) =M _(nom) +M _(slope) +M _(brake).

[0103] The portion M_(nom), as a rule, is known for a given vehicle. Itrepresents the nominal travel resistance on a plane surface in theabsence of a headwind or tailwind. To handle this nominal operatingstate, a transmission control system typically has a first array ofcharacteristic shift data for the selection of the appropriate gear.However, a control characteristic designed for traveling on a levelpavement is not suitable for uphill or downhill travel. It is thereforerecommended to use an overall travel-opposing torque M_(F) that alsoincludes the deviation from the nominal torque. According to theforegoing equation, the deviation from the nominal torque is representedby the sum of the braking torque M_(brake) and the torque M_(slope)caused by the gravity component in the direction of the slope angle. Asa matter of principle, the components M_(brake) and M_(slope) cannot beobserved independently of each other without additional sensors. In somevehicle types, the torque M_(brake) could be estimated from the sensorsignal of existing brake pressure sensors, but the majority of currentvehicles are equipped only with a brake light switch providing a signalB that is processed in the corrector block 350. In this case, thefollowing procedure can be used:

[0104] When the brake is not actuated, the brake torque is assumed to bezero. At the same time, the error signal e_(F) is used to continuouslyupdate the estimated value M_(slope)(R) in the corrector block 350 in ananalogous manner as the overall travel-opposing torque M_(F) in thefirst embodiment of the power train observer illustrated in FIG. 3b.

[0105] When a signal is received that the brake is actuated, the valueof M_(slope)(R) is frozen at the value that was last observed prior tothe actuation of the brake. The error information e_(F) is now used toestablish an estimated value M_(brake)(R) of the brake torque. Thus, thevalue for M_(slope)(R) remains available as a reference for selectingthe appropriate gear for mountain travel or in other travel situationsputting increased demands on the vehicle, where for example a lower gearneeds to be selected to provide more tractive torque.

[0106] As an advantageous possibility, the observer 301 can be expandedto include the features that an engine torque offset for the idlingcondition of the engine is compensated and/or a constant deviationbetween the torque requested by the driver and the actually deliveredtorque is taken into account in the control system for the clutch ortransmission. One can rely on the assumption that the engine torquesignal M_(e), as a rule, has a higher degree of relative accuracy thanabsolute accuracy and that even in a stationary operating state, i.e.,in a phase when the engine torque is substantially constant, there isoften a significant difference between the amount of torque requested bythe driver and the amount of torque that is actually delivered. Forexample when traveling in a mountainous terrain with large variations inaltitude, the amount of torque actually delivered for a given amount ofgas pedal depression varies in a wide range. If in this kind of travelsituation the clutch is engaged in accordance with a fixed torquecontrol characteristic, the resulting clutch engagement process can beuncomfortable to the vehicle occupants. The invention proposes a conceptto deal with this problem by introducing a factor k_(M) in a power trainobserver, for example in the power train observer of FIG. 3b, so thatthe currently achievable engine torque M_(e,current) can be estimatedfrom the amount of torque M_(e,request) ordered by the driver:

M _(e,current) ≈M _(e,current)(R)=k _(M) ·M _(e,request)

[0107] The factor k_(M) is adapted during substantially stationaryoperating phases by minimizing the difference between the estimatedquantity M_(e,current)(R) and the actually delivered engine torqueM_(e,current).

[0108] In an advantageous variation of the power train observer 301, amodel of the clutch characteristic is established during the slippingphases of the clutch. By combining the power train observer of theforegoing description with the model-supported variation, it is possibleto achieve advantages for the adaptation of the clutch characteristic aswell as for the results of the power train observer. It should be notedin particular that this offers the possibility to adapt the contactpoint (i.e., the engagement threshold) of the clutch during normaldriving, so that it becomes unnecessary to perform special engagementprocedures during suitable driving situations. During slipping phases ofthe clutch, the absolute amounts of transmittable clutch torque andactually transmitted clutch torque are identical. The transmitted clutchtorque can therefore also be determined from the clutch position x_(k)whose current value is available from the clutch control program or thetransmission control program, based on the function

|M_(k)(R)|=f(x_(k)).

[0109] It is advantageous if the control program for the automated shifttransmission performs adaptations of the contact point, the frictionvalue and/or the form factors, in order to continuously adapt the clutchcharacteristic to the current conditions of the vehicle, in particularto optimally follow the non-negligible fluctuations of the functionf(x_(k)) which is also referred to as the clutch characteristic.

[0110] A power train observer, for example of the type described in thecontext of FIG. 3b, can be advantageously implemented as a softwarealgorithm in the transmission control device or clutch control device107 (see FIG. 2). Of course, the program structure of the power trainobserver is implemented as a sequence of steps taking place in discretetime intervals. Consequently, an integration is performed as acumulative summation of signals that follow each other in discrete timeintervals.

[0111] The graph of FIG. 4a represents a friction value RW as a functionof the amount of time t_(A) that has elapsed since the engine or vehiclewas switched off. In the time interval t_(A), the clutch cools down sothat the physical friction value of the clutch changes. Therefore, thefriction value RW(T) that was adapted to a higher temperature level Tneeds to be adapted to the variable friction value of the clutch,reaching the value RW(I) if the clutch has cooled down to the ambienttemperature level. The aforementioned algorithm can work with a lineardecrease of the friction value as a function of t_(A) as represented bythe dash-dotted line 301, or it can decrease asymptotically to the endvalue RW(I), resembling a hyperbola in the shape of the curve 302. Whenthe vehicle is started up again while the clutch is still warm, theappropriate friction value is used in accordance with the time t_(A)that has elapsed since the vehicle or the engine was last switched off.Of course, the friction value RW as a function of the time span t_(A)during which the vehicle was turned off could also be stored in the formof characteristic data arrays. The data arrays could be established onthe basis of previous determinations of the clutch behavior, e.g., as afunction of the ambient temperature, of the vehicle load, the presenceor absence of a trailer, an operating profile containing such factors asgear shifts, acceleration and braking phases, traction of the wheels onthe pavement, trip duration, grade angle of the road, and similarfactors.

[0112]FIG. 4b illustrates another possibility of compensating thefriction value RW determined by a clutch control device after thevehicle has been turned off and subsequently restarted with the clutchstill warm. The determination of the friction value RW under thisalternative concept does not rely on the elapsed time since the vehiclewas turned off but uses instead a temperature-based model fordetermining the clutch temperature based on the engine temperature, forexample through a measurement of the coolant temperature. If the enginetemperature is close to the ambient temperature, the initial frictionvalue RW(I) is used. If the engine temperature is above the ambienttemperature, the clutch temperature T is derived from the enginetemperature, and the friction value is determined as a function of T asrepresented by the curve 303 in FIG. 3b, which is shown as a linearfunction but could also have a different curve shape.

What is claimed is:
 1. A method for controlling an automated clutch of amotor vehicle having an engine with a crankshaft and a transmission witha transmission input shaft and a transmission output shaft, wherein theautomated clutch is arranged to transmit a clutch torque between thecrankshaft and the transmission input shaft, and wherein during at leastone operating phase of the vehicle, the automated clutch is controlleddependent on an engine rpm-gradient (dn_(m)/dt), the method comprising:a) determining a first engine rpm-gradient signal (dn_(m)(M)/dt) basedon an engine torque signal (M_(e)) and a target value (M_(k)) of theclutch torque; b) recursively determining an engine rpm-rate signal(n_(m)(R)) based on said engine rpm-gradient signal; c) comparing anactual engine rpm-rate (n_(m)) to said engine rpm-rate signal (n_(m)(R))and determining a correction quantity K based on said comparison; and d)correcting said first engine rpm-gradient signal (dn_(m)(M)/dt) withsaid correction quantity.
 2. The method of claim 1, wherein the firstengine rpm-gradient signal (dn_(m)(M)/dt) is based on a torquedifference between the engine torque signal (M_(e)) and the target value(M_(k)) of the clutch torque.
 3. The method of claim 1, wherein thecorrection quantity K is based on a torque difference between the actualengine rpm-rate (n_(m)) and said engine rpm-rate signal (n_(m)(R)). 4.The method of claim 1, wherein the correction quantity K is assigned apredetermined weight in said correcting of the first engine rpm-gradientsignal.
 5. The method of claim 1, further comprising the step ofcompensating a time lag occurring between a time when a signal isgenerated and a time when said signal is used in the method.
 6. Themethod of claim 1, further comprising the step of compensating a timelag occurring between a time when the engine rpm-rate signal (n_(m)(R))is generated and a time when the actual rpm-rate (n_(m)) is determined.7. The method of claim 5, wherein the signal comprises the engine torquesignal (M_(e)).
 8. The method of claim 5, wherein the signal comprisesthe engine rpm-rate signal (n_(m)(R)).
 9. The method of claim 1, whereinthe engine rpm-gradient (dn_(m)/dt) is used to determine acharacteristic quantity of the clutch.
 10. The method of claim 9,wherein said characteristic quantity of the clutch comprises a frictionvalue (RW) approximating a physical friction value of the clutch.
 11. Amethod for controlling an automated clutch in a power train of a motorvehicle having an engine with a crankshaft and a transmission with atransmission input shaft and a transmission output shaft, wherein theautomated clutch is arranged between the crankshaft and the transmissioninput shaft, and wherein a torque to be transmitted from the engine tothe transmission is transmitted by means of a frictional engagementbetween a first clutch component that is rotationally fixed on thecrankshaft and a second clutch component that is rotationally fixed onthe transmission input shaft, wherein said frictional engagement ischaracterized at least by a physical friction value that changesdependent on an operating state of the clutch, the method comprising thestep of modeling the physical friction value as a friction value (RW) ina clutch control unit based on at least one parameter of the powertrain, wherein the friction value (RW) contains a component representinga dependency of the friction value from a clutch temperature.
 12. Themethod of claim 11, further comprising the step of measuring the clutchtemperature by means of a temperature sensor.
 13. The method of claim11, further comprising the step of determining the clutch temperature bymeans of a temperature model, wherein at least one of a transmissiontemperature, an engine temperature, an ambient temperature, an enginecoolant temperature, and an elapsed time since the engine was lastturned off is taken into account.
 14. The method of claim 11, wherein alimit for a maximum amount of change of the friction value is set as afunction of the clutch temperature.
 15. The method of claim 14, whereinsaid maximum amount is set as a limit value for a rate of change of theclutch temperature.
 16. The method of claim 14, wherein said maximumamount is adjustable.
 17. The method of claim 16, wherein said maximumamount is adjustable as a function of the clutch temperature.
 18. Themethod of claim 14, further comprising the steps of storing a set ofdata relating to the clutch temperature when the vehicle is switchedoff; retrieving said data when the vehicle is switched on again, anddetermining a current friction value based on said data.
 19. The methodof claim 18, wherein said maximum amount is adjusted if and when thevehicle is switched on at a time when the clutch temperature is stillsignificantly warmer than the ambient temperature.
 20. The method ofclaim 18, wherein the current friction value is determined based furtheron an amount of time elapsed since the vehicle was last switched off.21. The method of claim 18, wherein the current friction value isdetermined based further on an actual clutch temperature existing at atime when the vehicle is switched on again.
 22. The method of claim 20,wherein the current friction value is determined based on an assumptionthat the current friction value has a linear relationship to the amountof time elapsed since the vehicle was last switched off.
 23. The methodof claim 20, wherein the current friction value is determined based onan assumption that with increasing time since the vehicle was lastswitched off, the current friction value asymptotically convergestowards an ambient-temperature friction value.
 24. The method of claim1, further comprising the steps of determining and correcting amovement-opposing torque of the vehicle.
 25. The method of claim 24,wherein the movement-opposing torque is corrected by means of correctionvalues that are given as a characteristic curve in function of an airresistance.
 26. The method of claim 24, wherein the movement-opposingtorque is corrected dependent on a grade angle of a road being traveledby the vehicle.
 27. The method of claim 24, wherein themovement-opposing torque is corrected by means of a correction signal,and wherein said correction signal is determined based on at least oneerror between an estimated value and an actual value of at least onequantity.
 28. The method of claim 27, wherein the at least one quantitycomprises an engine rpm-rate, wherein the estimated value is based on aneffective engine torque, and wherein the at least one error comprises afirst error based on a comparison between the estimated value and theactual value of the engine rpm-rate.
 29. The method of claim 27, whereinthe at least one quantity comprises comprises a traveling-speed relatedquantity, wherein the estimated quantity is based on an effective enginetorque, and wherein the at least one error comprises a second errorbased on a comparison between the estimated value and the actual valueof the traveling-speed related quantity.
 30. The method of claim 29,wherein the traveling-speed related quantity comprises a wheel rpm-rate.31. The method of claim 29, wherein the effective engine torque iscorrected with an estimated value for a transmitted clutch torque. 32.The method of claim 28, wherein said first error is used to correct atleast one estimated quantity.
 33. The method of claim 29, wherein saidsecond error is used to correct at least one estimated quantity.